Shell-and-tube heat exchangers
| Deviation | Typical causes | Typical consequences | Typical safeguards |
|---|---|---|---|
| Tube rupture | Corrosion, vibration, thermal fatigue | High-pressure fluid enters the low-pressure side: overpressure | Low-pressure side relief sized for tube rupture where the design pressure ratio requires it |
| High temperature on the cold side | Loss of cold fluid flow; bypass closed | Vaporisation, vibration, overpressure | Temperature alarm; low flow alarm |
| Blocked-in cold side with hot side flowing | Isolation valves closed during operation or maintenance | Thermal expansion overpressure | Thermal relief valve; procedure |
| Fouling | Long run length | Lower duty, higher firing elsewhere | Monitoring of ΔP and outlet temperature |
| Leak to cooling water | Tube leak | Hydrocarbon in cooling water, release at cooling tower | Cooling water monitoring |
Distillation columns
| Deviation | Typical causes | Typical consequences | Typical safeguards |
|---|---|---|---|
| High pressure | Loss of cooling to the condenser; reflux pump failure; excess reboiler heat | Overpressure; relief to flare | Pressure control; high pressure alarm; reboiler heat cut-off SIF; relief valve |
| High level in the bottom | Bottom pump failure; level control failure | Liquid on the reboiler return, flooding, carry-over | Level alarm; high-high level trip of feed |
| Low level in the bottom | Level control fails open | Pump cavitation; vapour blow-through to downstream | Low-low level trip |
| Loss of reflux | Pump trip | Off-spec product, temperature rise at top | Low flow alarm |
| Start-up with high level | Level instrument out of service, filling without draw-off | Overfill to relief system, release | Independent high level alarm; start-up checks of instruments |
The last row is not hypothetical: see the knowledge article on the Texas City refinery incident (2005).
Written for First Out AI as engineering guidance. It supports engineering work and does not replace it; check every value against your standards, certificates and company rules with a competent functional safety engineer.